The extracellular matrix
The structural and signaling scaffold cells build around themselves — and the template engineered scaffolds try to imitate.
The extracellular matrix (ECM) is the material cells secrete and live within: collagens, proteoglycans, glycosaminoglycans, and adhesion proteins such as fibronectin and laminin. It was long treated as inert packing material. It is not. The ECM stores growth factors, presents binding sites that let cells anchor and pull, and transmits the mechanical forces that shape cell behaviour.
Because cells read the matrix, its stiffness and composition can steer differentiation on their own — stem cells cultured on stiff substrates tend toward bone-like lineages, softer ones toward other fates. That principle underlies much of Scaffold design principles: an engineered scaffold is an attempt to reproduce enough of the ECM's instructions to get the right result. It also explains the appeal of Decellularized matrices, which start from real tissue and strip the cells away, keeping the native architecture.
In bone, the mineralised ECM is also a reservoir: factors such as BMPs and TGF-β are bound within it and released during remodeling.
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